1. Field of the Invention
The invention relates to an internal combustion engine equipped with a variable valve train capable of arbitrarily altering the opening and closing timing and/or the opening amount of at least one of an intake valve and exhaust valve. In particular, the invention relates to a technology for favorably generating intake pipe negative pressure in an intake passage in an internal combustion engine.
2. Description of the Related Art
Recent years have seen the development of internal combustion engines equipped with a variable valve train capable of altering the opening and closing timing and/or the opening amount of at least one of an intake valve and exhaust valve in an internal combustion engine mounted in a vehicle or the like for the purpose of improvement in brake thermal efficiency, improvement in exhaust emission, reduction in specific fuel consumption, or the like.
An internal combustion engine provided with an intake and exhaust valve driven to open and close by electromagnetic force, i.e. what is known as an electromagnetic valve train, is known as an example of a variable valve train. In an internal combustion engine provided with this type of electromagnetic valve train, because there is no need to drive the intake and exhaust valve to open and close using the rotation force of the engine output shaft, mechanical loss originating in the drive of the intake and exhaust valve is prevented. Moreover, in the internal combustion engine provided with the electromagnetic valve train, it is possible to arbitrarily alter the valve opening time and the opening and closing timing of the intake and exhaust valve, so that pump loss of the internal combustion engine caused by a throttle valve can be suppressed.
However, in a non-throttle operation-controlled internal combustion engine, because almost no pump loss of the internal combustion engine is generated, there is no negative pressure in the combustion chamber of the internal combustion engine during deceleration of the vehicle. As a result, the problem arises that the engine braking effect is diminished.
In response to this, control methods for internal combustion engines, such as that described in JP Laid-Open No. HEI 10-331671, have been proposed. The control method for an internal combustion engine described in the above publication aims at increasing the engine braking effect in an internal combustion engine provided with electromagnetic intake and exhaust valves and non-throttle operation-controlled with these electromagnetic valves. In this control method, the electromagnetic valves are controlled to increase the pump loss of the internal combustion engine. Thus, negative pressure is generated within the cylinders of the internal combustion engine, thereby increasing the engine brake effect.